I have five week old Buttercups, too, and judging that one against mine, I think you may have a roo. Mine have the little "crown" also but they are much much smaller than that.
I'm crossing my fingers for you though!

Judging by the color of its feathers, I think your chick is a girl. Buttercup hens and roosters have different colored feathers-the hens are salmon colored in front and speckled in the back, and the roosters are mostly a red color. I have seven full grown Buttercups at the moment, and your Buttercup chick definitely looks like my Buttercup hens-NOT the roosters!

What breeds are your other chickies? I just some more Buttercup chicks along with some golden Lakenvelders and Dominques and the Buttercups are much bolder than the rest so her dominance could just be the breed!

She's with ameracaunas, black spanish and cochin, 7 total. She is definitely more aggressive... it looks as though she's getting little wattles now too, unlike the others. UGH! I will be heart broken if I have to give up another chicken.

You need to watch for a splash of red on their back. If it starts turning red on her/his back then it will be a roo. They look exactly alike for weeks till the roo suddenly starts getting in his roo colors the breast feathers will be red also. But the color change will start on their back. Females won't get the salmon look till the have a secondary growth of feathers. By the time they are laying they will look like they should. Keep watching. If you see a splotch of red on their backs then its definately a roo.